In conventional total hip arthroplasty, the head and neck of the natural femur are removed and replaced with an artificial femoral head and neck. The artificial head and neck are attached to a stem that is secured in the intramedullary canal of the femur. Over the years total hip arthroplasty has had excellent clinical success. However, various conditions can arise in which it becomes necessary to perform revision surgery on the hip joint. The presence of the implant in the femur can sometimes result in stress shielding, osteolysis or other conditions that lead to the gradual loss of bone stock and loosening of the implant. An infection may require removal of the implant. Additionally, the useful life of an artificial hip joint is about 15 to 25 years, and a young hip patient will therefore typically require a revision surgery at some point in his or her lifetime.
When performing a revision hip procedure, it is desirable to have as much bone stock available as possible. Accordingly, efforts have been made to develop surface replacement arthroplasty procedures that preserve bone stock in hip procedures. In surface replacement arthroplasty of the hip, the natural femoral head and neck are preserved, but are resurfaced to receive an artificial femoral head. An example of such a femoral head for use in surface replacement arthroplasty procedures is shown in FIGS. 1, 2, 7 and 8 of U.S. Pat. No. 6,156,069 (Amstutz), which is incorporated herein by reference. As shown in FIG. 1 of Amstutz, the femoral head includes a central tapered stem and a spherical surface replacement portion. An inner surface of the prosthesis covers the reamed bone of the femoral head, while the central tapered stem is centered in the femoral head and neck. Femoral heads of the type shown in Amstutz are available from Wright Medical Technology, Inc., 5677 Airline Road, Arlington, Tenn. 38002.
In one technique of surface replacement arthroplasty, the surfacing of the femoral head and the resulting positioning of the femoral component are based on the placement of a guide pin in the femoral neck and head. The surgeon opens the hip, dislocates the femur, and then centers the guide pin in the femoral head and neck using an antegrade approach. The guide pin protrudes from the femoral head, and is used to orient surfacing instruments. Amstutz provides views of a guide pin centered in the head and neck of a femur (FIGS. 9 and 10 of U.S. Pat. No. 6,153,069). Amstutz further describes instruments and techniques for accurate placement of the guide pin, along with use of the guide pin to surface the femoral head for receipt of the femoral implant.
Because surfacing of the femoral head is based on the position of the guide pin, accurate placement of the guide pin in the femoral head and neck is critical in surface replacement arthroplasty techniques such as those described in Amstutz. However, assessing the femoral head-neck relationship intra-operatively after dislocation and then placing the guide pin in an antegrade fashion can be somewhat complicated and unreliable. A relatively large exposure is required, particularly for inexperienced surgeons. A large exposure increases bleeding, pain and the risk of infection.
The present invention improves on prior art surface replacement arthroplasty by incorporating a retrograde approach for centering the guide pin. Retrograde approaches are used in hip fracture fixation using plates and a cannulated lag screw. A guide pin is placed retrograde into the desired position within the femoral neck and head. The procedure takes about ten minutes and is accomplished with the patient in a supine position using image guidance (i.e. C-arm). The guide pin is then used to place the cannulated lag screw. An example of one such femoral fracture fixation technique is discussed in U.S. Pat. No. 4,522,201 (Tongue).
Retrograde approaches have also been used to drive resurfacing instruments located in the hip via a driveshaft located in the femoral head and neck. The resurfacing instruments are introduced through a main incision, and are connected to the end of a driver that is inserted retrograde through a channel formed in the femoral head and neck. U.S. Patent Application Publication 2003/0028196 (Bonutti) teaches a technique for reaming the acetabulum using a drive shaft disposed in the femoral head and neck (see particularly FIGS. 68-73). U.K. Patent 2,372,302 (McMinn) teaches a similar technique for resurfacing the femoral head (see particularly FIGS. 4-6). As shown in FIG. 2 of McMinn, a guide-wire is inserted through the lateral aspect of the femur and up into the femoral head and neck, with the desired position obtained using either an external alignment jig, a navigation system, or x-ray control. Following insertion of the guide-wire, the femoral head is dislocated from the acetabulum. The guide-wire is then over-drilled, producing a canal, typically of 8.5 mm in diameter, up the femur, femoral neck, and exiting through the zenith of the femoral head. Once the canal has been completed, the drill is removed and preparation of the femoral head is then commenced. The first step in femoral head preparation, shown in FIG. 4 of McMinn, is the insertion of a drive rod up the canal in the femur. An appropriately sized sleeve cutter of generally hollow cup shape is inserted through the main incision and releasably secured to the end of the drive rod, which extends out of the top of the femoral head. The rod is driven by any suitable power means and the cutter advanced down onto the femoral head so that the periphery thereof is thus resected. The cutter is then unscrewed and removed via the main incision, with the drive rod being removed via the femoral neck incision. The next method step, shown in FIG. 5, involves the application of a sleeve resection guide to the periphery of the femoral head, with the guide being inserted through the main incision. An appropriate amount of zenith of the femoral head, as determined by the positioning of the guide, is then resected using a powered cutting blade, thereby maintaining the patient's correct leg length. After completion, the guide is removed through the main incision. The drive rod is then again inserted through the femoral neck incision and up along the canal so that the threaded end of the drive rod extends from the top of the resected femoral head. As indicated in FIG. 6 of McMinn, an appropriately sized chamfer cutter is then inserted through the main incision and attached to the end of the drive rod. The drive rod is moved down the canal so that the cutter is brought down onto the femoral head so that when the drive rod is powered to rotate, the cutter similarly rotates and cuts the femoral head to provide a chamfer thereon. Once the chamfering of the femoral head shown in FIG. 6 has been carried out, the femoral head preparation is complete.
Prior art techniques such as Bonutti and McMinn form a large hole in the lateral cortex and into the head and neck for direct retrograde access of cutting instruments. Such large holes may lead to fracture in the sub-trochanteric region. Additionally, the procedures are not done preoperatively, and do not provide teachings concerning the placement of guide pins for use in surface replacement arthoroscopy of the type described in Amstutz.
As far as the inventor is aware, retrograde approaches have not been used to center guide pins for use in surface replacement arthroplasty. There if thus a need for the novel approach for pin guide placement presented herein.